def test_list_subtract_recover(xs, ys):
missing = list_subtract(xs, ys)
zs = list(ys)
zs.extend([xs[i] for i in missing])
assert list(list_subtract(xs, zs)) == []
def test_list_subtract_same_list(xs):
assert list(list_subtract(xs, xs)) == []
ys = list(xs)
random.shuffle(ys)
assert list(list_subtract(xs, ys)) == []